In an electrophotographic image forming apparatus, there is known a structure in which elements such as a photosensitive drum and a developing roller, which are rotatable members related to image formation, are integrated into a cartridge which is detachably mountable relative to a main assembly of an image forming apparatus (hereinafter, the apparatus main assembly). In such a structure, a structure for receiving a driving force from the apparatus main assembly to rotate the photosensitive drum in the cartridge is employed in many apparatuses. At this time, a structure is known in which a driving force is transmitted through engagement between a coupling member on a cartridge side and a driving force transmitting portion such as a drive pin on the apparatus main assembly side.
For example, Japanese laid-open Patent Application No. 2008-233867 discloses a cartridge having a coupling member provided at an end portion of a photosensitive drum so as to be tiltable with respect to a rotation axis of the photosensitive drum.